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Depth of Field
What is it ?
More accurately described as Depth of Focus it is the area in front
of and behind the subject that appears in focus, i.e. not fuzzy or
blurred.
Why
should we care
Why
should we care
Often in landscape photography
we would like to have the entire picture, foreground, middle, and background
all in focus. Therefore we
strive for great depth of field. Yet
in portraits we would often like to blur the background to de-emphasize busy
or otherwise distracting backgrounds. In this case we want to keep the
subject sharp and have the background go soft.
We can do this by choosing a narrow i.e. short depth of field.
How can we
control depth of field?
By controlling the aperture
used in taking the photograph.
OK, what’s an
aperture?
It’s a hole! It is the size
of the lens opening that lets in the light. Inscribed on your lens and/or displayed on your camera it’s the f-numbers
(referred to as f stops). f
2.0, f 2.8, f 4, f 5.6, f 8, etc. Those
numbers really describe a ratio of the lens focal length vs. the size of the
opening. A 50mm lens with an
aperture of 25mm is f 2.0. (50 ÷25 = 2)
A 50mm lens set to an aperture of 12.5mm is f 4.0.
(50 ÷ 12.5 = 4) That
same lens set to a 6 mm opening is f 8. (50 ÷ 6 .8)
Notice as the hole gets smaller the
f-numbers become larger.
f 2 provides a 25 mm aperture (in a 50mm lens) while f 8 provides
only a 6 mm aperture.
The smaller the hole (aperture)
the greater the depth of field (dof).
F 4 provides a greater depth of
field than f 2. F 8 provides an
even greater dof. Want to blur
the background, foreground or both? Choose a small f-number.
Want to keep everything in focus?
Choose a high f-number. Stated
another way:
The higher the f stop the greater the depth of
field.
Hint: Whatever depth of field (dof) you choose, it is never positioned
equally in front of and behind the subject.
About one third is in front of the subject and two thirds are behind
the subject. So to get the
greatest dof in a landscape choose a high f stop and focus about one third
into the scene
Exposure
Of course it’s a combination
of aperture and shutter speed that determines the amount of light reaching
the film or digital sensor. . F
8 @ 1/60 will give you the same exposure as f 2 @ 1/1000 but the f 8 1/60
choice will provide greater dof. So
if you choose a high f number for greater dof, the resulting small
aperture lets in less light. So the shutter speed must be longer to allow enough light to reach the film or
sensor. Set your camera to
Aperture Preferred. That lets
you chose the aperture and the camera will automatically select an
appropriate shutter speed.
Hint: You
can check your depth of field by pressing the Depth of Field Preview button
on your camera while looking through the viewfinder (on SLR cameras).
But notice the viewfinder loses brightness.
This is because the lens is wide open while focusing and composing
but stops down to the “taking” aperture when the photo is exposed or
when the dof button is pressed. good
luck and good shooting!
Ron James
FILE FORMATS
.JPEG, .RAW, .TIFF, .PSD- which should you use?
By Nels Hebgen
File formats are the various ways your camera and computer will save your camera and computer data for future use in a form recognizable by your computer. Modern digital cameras will save picture data in .JPEG format. More advanced cameras offer .RAW, or .RAW plus .JPEG. Once in your computer, You have the option of saving your computer files as .TIFF and .PSD files to a disk or hard drive. There are other file formats you could use, but these two are the most universally acceptable for photographs. For most everyday shooting and snapshots, .JPEG is adequate, but to get the most out of your photos, .RAW offers much more than .JPEG.
.JPEG is a compressed format. That means that the software, either in your camera or computer, takes a the raw picture data and compresses it into a smaller space. JPEG files are much smaller than .RAW, .TIFF, or .PSD files. In the initial compression process in your camera or computer, JPEG loses about 1/3 of the original data in the compression process. If you open and close a .JPEG file many times, you will note a slight dcrease in file size each time you save it. This is because each compression throws away another small piece of the file data. On the positive side, you would have to do this MANY times to notice any difference in picture quality. .JPEG files are processed by the camera, and will show a better thumbnail than .RAW file thumbnails, which are processed only minimally, and thus do not initially look as good as .JPEGS.
| JPEG
advantages |
JPEG disadvantages: |
| 1. Small file sizes |
1. Loss of data |
| 2. Adequate for most
shooting |
2. Initial Processing in camera.(?) |
| 3. Initial processing in
camera.(? |
3. Not as much data to work with as
RAM |
| 4. Better looking thumbnails |
4. Can overwrite file, losing original data. |
One partial solution to the data loss problem with .JPEGS is to always use the same original file, and NOT resave that original file. There is no way round the initial 1/3 loss of date in the original compression the first time a .JPEG file is saved. .JPEGS are quite adequate, and work well for most everyday shots, but do not have the latitude of data necessary for the fine and critical manipulation needed by many advanced amateurs and professional photographers.
ALL the original data is in the .RAW file, and available to the photographer. You cannot overwrite a .RAW file, so you always have a protected original digital negative. After opening a .RAW file, you must save it in another format, such as .JPEG, .TIFF, or .PSD. You cannot save any file as a .RAW file. To take full advantage of the additional data available with .RAW files, you need to do your own photo editing in Photoshop or another photo editor. It is much easier to pull data out of over exposed highlights and/or underexposed shadows in a .RAW file than in a .JPEG file. .RAW files have a wider tonal latitude.
One minor problem with .RAW files is that each camera manufacturer uses a different proprietary format for its raw files. Canon raw files are .CR2. Nikons are something else. Adobe has been pushing a new format, .DNG, as a universal format for raw files, but is is not gaining much acceptance. If you have a new camera, it may be necessary to download the latest raw reader from Adobe, so that your Adobe applications will recognize your raw format.
| RAW advantages: |
RAW disadvantages |
| 1. All data captured always available |
1. Large files |
| 2. Cannot over write- Always have your protected original digital negative. |
2. Thumbnails not processed |
| 3. Easier and better processing
Better retrieval of shadows/highlite |
3. Different RAW formats from different camera details manufacturers and highlights. . |
.TIFF, .PSD, and .JPEG are all optional formats in which you can save .RAW files in. .TIFF is an older but pretty universal accepted format, and is not a compressed file format, so saves all your data available. .PSD is a Photoshop format. It is useful if you use Photoshop or other Adobe applications, as it can save such things as layers, which .TIFF will not necessarily do. Saving as .JPEG has all the pitfalls and disadvantages discussed previously.
In summary, .JPEG files are fine for many photographers, especially if you do not open and save the same file many times. .RAW files give you much more data and latitude and ability to manipulate your photos, at the price of larger files. .JPEGs are probably your best choice for use on the web or for email, as the smaller file is an advantage and high quality is not needed.
You can safely save both .RAW and .JPEG files as .TIFFs or .PSDs, depending on your needs. This, of course, will solve a lot of the .JPEG repeated saving problem, but not the initial loss of data in .JPEGS. Note that most of the time you will not miss that initial lost data. You will not be able to see the difference until you attempt more advanced editing. If you are using Photoshop, or other Adobe applications, in any of its various configurations, I suggest you save your .RAW and/or .JPEG files as .PSD files, the native format for all Adobe applications.
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